1. Field
Embodiments of the present invention relate to a nonvolatile semiconductor memory device.
2. Description of the Related Art
In recent years, ReRAM (Resistive RAM) is receiving attention as a technology for realizing an even higher level of integration in nonvolatile semiconductor memory devices.
A memory cell array in this ReRAM is configured having a variable resistance element and a rectifier element such as a diode or the like which is a selection element connected in series. The variable resistance element has at least two resistance states, and switching of these resistance states is performed by voltage application to the variable resistance element. Moreover, the case where voltages of the same polarity are used when switching between these two resistance states is called a unipolar operation, and the case where voltages of different polarities are used when switching between these two resistance states is called a bipolar operation.
In the case that, of these two operations, a bipolar operation is performed, the diode or the like which is the rectifier element requires to have the following two conflicting properties, namely that when a reverse direction bias is applied to an unselected memory cell, an off leak current flowing in the unselected memory cell is kept small, and that when a reverse direction bias is applied to a selected memory cell, the selected memory cell can be supplied with an operation current required for switching of the resistance state of the variable resistance element.